casting with Union types

[bakesteve]

trying to figure the right way to get flow to recognise this code where I can pass in a Date or a moment

I cant use native js typeofs as far as I can tell.
Know I could just do moment(date).format(...) but while moment is pretty efficient here, feels like there should be a better way to tell flow that isMoment is (basically) a type checking function?

  if(moment.isMoment(date)){
      return date.format(this.props.displayFormat); 
// call of method format Property not found in  [LIB] core.js:166:1,214:1: Date
    }else{
      return moment(date, this.props.inputFormat).format(this.props.displayFormat);
    }

[gabelevi]

Yeah, this is on our minds too. We'd love a way to declare the refinements that a user space function might make to a type. Ideally you'd be able to declare something like

isMoment(x: any): x is moment { ... }

which would tell Flow that if isMoment is true then the argument is a moment.

[gabelevi]

Tracking this issue in #34